1. Field of the Invention
The present invention relates to an imaging-device driving unit that orders an imaging device to speedily discharge an unnecessary electrical charge generated by a charge-transfer channel, such as a CCD, before a photographing operation.
2. Description of the Related Art
Various kinds of imaging devices which generate an image signal corresponding to an optical image of a subject are known. Among the various kinds of imaging devices, a CCD imaging device which is improved with respect to size, S/N ratio, sensitivity, and aspects is broadly used.
A CCD imaging device outputs pixel signals according to the amount of light received by the pixels, by ordering a vertical CCD to receive signal charges generated by a plurality of pixels separately, and ordering the vertical CCD to transfer the signal charges to a horizontal CCD, and also ordering the horizontal CCD to transfer the signal charges to an output amplifier.
The vertical CCD happens to store an electrical charge generated by the vertical CCD itself based on light leaked to the vertical CCD, and from an electrical charge left upon transferring an electrical charge exceeding the transferring capacity, from an electrical charge leaked from a pixel, and so on. Such an electrical charge become noise in a signal charge, and should be discharged to display an accurate image.
Japanese Unexamined Patent Publication No. H04-356879 discloses the speedy discharge of an electrical charge remaining in the vertical CCD before the vertical CCD receives signal charges from pixels and transfers them.
On the other hand, the frequency of a driving signal used to drive the vertical CCD should be raised in order for the vertical CCD to speedily discharge. However, power consumption increases with the rise in frequency, reducing the power available for photographing operations, and possibly resulting in the suspension of the photographing operation.